1. Field of the Invention
The present invention relates to a medical bag having excellent sanitariness, flexibility, transparency, and heat-resistance and suitable for use as a container of blood and various medicinal liquids. More specifically, it relates to a medical bag composed of a laminate comprising (i) an inner layer, (ii) an intermediate layer, and (iii) an outer layer. The interlayer is derived from an ethylene-1-olefin copolymer having a density of 0.935 g/cm.sup.3 or less and the inner and outer layers are independently derived from a polymer selected from the group consisting of low-density polyethylenes, linear low-density ethylene copolymers, and high-density polyethylenes.
2. Description of the Related Art
Rigid containers made of, for example, glass, polyethylene, and polypropylene, and flexible (or non-rigid) bags made of, for example, poly(vinyl chloride) containing plasticizers are heretofore known as medical containers or bags. The rigid containers, however, have a disadvantage in that air is introduced into the containers by using a transfusion set provided with a vent needle or hole when the liquid contained therein is dropwise introduced into a human body through, for example, a vein, and therefore, the liquid contained therein might be contaminated and air can enter the vein to cause an air embolus therein. Thus, these rigid containers do not completely satisfy the requirements of sanitariness and safety. On the other hand, flexible bags have advantages in that the introduction of air is not required, the bag itself is naturally compressed under atmospheric pressure with the dropwise introduction of the liquid contained therein, the introduction of air contained in the bag into a human body does not occur since the liquid contained therein fills the bottom of the bag at the completion of transfusion, a rapid transfusion can be carried out under pressure, and the bags is not bulky, unlike containers, and therefore, the transportation thereof is easy. For these reasons, the use of the flexible bags as medical containers or bags has increased. The use of these flexible bags, especially those made of non-rigid poly(vinyl chloride), however, involves possible problems caused by the migration of plasticizers into the liquid contained in the bags and the toxicity of the vinyl chloride monomer contained in poly(vinyl chloride).
Japanese Unexamined Patent Publication (Kokai) No. 58-165866 proposed a medical bag composed of a laminate comprising, as an intermediate layer, ethylene-vinyl acetate copolymer, ethylene-propylene type elastomer, or ethylene-butene-1 type elastomer. But, although this medical bag has excellent sanitariness, flexibility, and transparency, the heat-resistance thereof is low and thus the appearance thereof is not satisfactory due to the generation of wrinkles and of failures in the bag when, for example, the bag is subjected to a sterilization treatment temperature (e.g., 121.degree. C. or more).